This project will study the effects of exercise during pregnancy on reproductive function in offspring, using a rat model. Many athletic women want to continue exercising when they become pregnant, and exercise is generally considered beneficial for healthy mothers. There are no known major detrimental or beneficial effects of maternal exercise on fetuses, but current knowledge is limited and superficial. Animal studies show that maternal stresses other than exercise can adversely affect gonadal function, estrous cyclicity, sexual behavior, and fertility in female and male adult offspring. These effects are presumed to result from stress-induced activation of the maternal, and possibly fetal, hypothalamic-pituitary-adrenocortical axis (HPAA); hormone actions appear to be mainly on the developing fetal brain. Activation of the HPAA also results in adrenocortical androgen secretion; these androgens may affect sexual differentiation of the developing brain. Secretion of all these hormones is stimulated in exercising females. Thus there is a potential for maternal exercise-induced alterations, possibly quite subtle, in the development of mechanisms controlling reproductive functions in the fetus. This proposal includes six experiments which will examine the effect of maternal exercise on reproductive variables in offspring and hormonal changes in fetuses during maternal exercise. In Experiment 1, female and male offspring of exercised and sedentary mothers will be followed through adulthood, with observations on a broad range of reproductive parameters, including neonatal anogenital distance, age at vaginal opening, estrous cyclicity, fertility, and pup survival. Experiment 2 will look for subtle effects of maternal exercise on sexual behavior by subjecting female and male offspring of exercised and sedentary mothers to castration, hormone replacement, and behavior testing. In Experiments 3 and 4, concentrations of corticosterone and androstenedione, respectively, will be measured in blood samples taken from mothers and fetuses immediately post-exercise or at rest. Experiments 5 and 6 will reduce the effects of exercise-induced secretion of corticosterone and androgens, respectively, by administering antagonistic drugs prior to each maternal exercise session and examining the offspring reproductive variables studied in Experiments 1 and 2. Together these studies will provide insight about whether offspring reproductive parameters are affected by maternal exercise and whether exercise-induced elevations in corticosterone or androgens contribute to these effects.